1. Field of the Invention
The present invention relates to a light spot position measuring method, wherein a position or positions of a point light source or point light sources which directly or indirectly emits/emit light is/are measured using a two-dimensional image pickup device. More specifically, the present invention relates to a technique for measuring the position or positions of the point light source or sources with improved accuracy.
2. Description of the Prior Art
Conventionally, when detecting a two-dimensional position of an observation point identified by a point light source on a plane, for example, two beam-direction detectors each formed by combining a one-dimensional image pickup device, such as, a linear image sensor and a slit or a lens, are used to derive a position of the point light source (hereinafter also referred to as "light spot position") using the method of triangulation. For increasing the measurement accuracy to a practical level in such a light spot position measurement, it is necessary to improve the resolution of the linear image sensor. At present, a commercially available linear image sensor has about 10,000 picture elements (pixels) at the maximum. In order to ensure the measurement accuracy of the practical level in, such as, the survey in the civil engineering field, an ultrahigh-density one-dimensional image pickup device having about 100,000 pixels is required.
On the other hand, when detecting a three-dimensional position of a target in the form of a point light source, the so-called stereo method has been widely used, wherein two television cameras each including a two-dimensional image pickup device, such as, an area image sensor are used. In this case, improvement in the measurement accuracy faces further difficulty since, for improving the resolution of the area image sensor, the number of pixels is required to be increased in a square rate.
Technique has been proposed as disclosed in, such as, Japanese Second (examined) Patent Publication No. 3-31362, for improving an apparent or effective resolution of the television camera without actually increasing the number of the pixels of the area image sensor. According to this technique, a cross filter is mounted to a lens of the television camera so as to convert a light beam from a point light source into a cross-shaped streak image through the cross filter. The cross-shaped streak image is projected onto a pixel array of the area image sensor. The projected image is processed to derive an intersection point of two straight lines included in the cross-shaped streak image for determining a position of the point light source.